A man jailed for killing his lover's husband was denied a fair trial by having his mother prosecuted alongside him, the Court of Appeal has heard.

Lawyers for Roger Ferguson also claimed directions to the jury who found him guilty of murdering Paul Crymble were prejudicial and inadequate.

Ferguson (33) was ordered to serve at least 18 years in prison for his role in suffocating the father-of-two with a plastic bag in June 2004.

Jacqueline Crymble (37), the victim's wife with whom Ferguson was having an affair, was also convicted of the murder.

As the former lovers launched legal bids to have the guilty verdicts overturned, judges were yesterday told Ferguson's mother should have been tried separately.

Dawn Ferguson was found guilty of attempting to pervert the course of justice by giving her son a false alibi.

But Frank O'Donoghue QC, for Co Armagh man Roger Ferguson, argued that having her as a co-defendant rendered the trial process unfair.

He said: “In the context of this case, the prosecution of Dawn Ferguson alongside the applicant fatally undermined the ability of the applicant to put his alibi evidence fairly before the jury, so the jury could assess the evidence against the circumstantial evidence upon which the prosecution relied.

“Effectively, the witness was condemned by the prosecution even before she gave evidence.”

Ferguson, from Tandragee, Armagh, claimed he was at home in bed on the night 35-year-old Mr Crymble was killed.

Jacqueline Crymble alleged four masked men broke into the family home on Ballybrae Road near Richhill, Armagh, looking for drugs and money before attacking and kidnapping her husband.

But low copy number DNA techniques established the chances that a profile found on cable ties used to bind Mr Crymble belonged to anyone other than Ferguson were a billion to one. The Court of Appeal heard Ferguson lied to hide the fact he was in a sexual relationship with Jacqueline Crymble.

Other evidence against the pair included telephone calls and a visit they made to a car showroom to inquire about buying a jeep — allegedly with the proceeds of an insurance claim to be made after the victim's death.

Colin Robinson, a co-accused who was cleared of murder but found guilty of assisting an offender, gave evidence about events leading up to the murder.

He said Ferguson had asked him to go to Paul Crymble's house to “give him a bit of a rattle” and described the victim's wife as “hardened” and “somebody to keep away from”, judges were told.

Mr O'Donoghue contended: “In terms of characterising it (Robinson's evidence), it could not be more damning of a co-accused.”

He added: “The type of evidence this man was giving was such that there should have been a very, very clear warning given (to the jury). The warning was wholly deficient with regard to them both.”

Ferguson sat expressionless alongside Crymble in the court as other grounds of his appeal were outlined. His barrister levelled further criticisms at jury directions and claimed the offence of manslaughter should have been left with them. The application for leave to appeal against convictions was adjourned until today, when lawyers for Crymble are expected to open their case.